Pavement Type And Structure Engineering Essay

Highway pavings are known of its two chief types which are flexible paving and stiff paving. Flexible paving is the paving made of bitumen, whilst stiff paving is the paving made of Portland cement concrete. Concrete in nature are known of its durable life-time in constructions, similarly, concrete paving excessively, of its long structural life. However, the chief concern for stiff paving is to supply a lasting surface with equal clash that is economical and safe. Surface clash may perchance cut down over clip due to smoothing consequence of surface due to go throughing traffic and weathering. In route design, surface clash and pavement texture are indispensable qualities to be highlighted on as their characteristic correlatives with the latter route paving public presentation in run intoing the high manner design standards and safety. This is of import as it could do loss of life.

Many factors affect the surface clash at the tyre paving interface such as the type of tyre, tread form, tyre force per unit area, tyre status and so on. Pavement surface types and vehicle tyres are major subscribers to pavement clash. Tires in hapless status with worn paces, or improper rising prices, will non hold equal braking clash on any pavement surface.

Furthermore, the research done by Kuttesch ( 2004 ) cited by Davis ( 2001 ) explained that accidents occurred from legion lending factors including driver mistake, hapless geometric alliance of the roadway, and a deficiency of sufficient clash at the tyre paving interface during wet conditions. In farther research by Davis ( 2001 ) mentioned about the wet on the pavement surface may forestall vehicle tyres from doing equal contact with the route surface.

Surface dressing is a route surface intervention if sufficient attention is taken in the planning and executing of the work. In pavement design there are two of import features need to see which skid opposition and texture deepness. Accidents occurred due to several grounds such as driver mistake, vehicle failure, and clash lacks at the tyre paving interface. Accidents occur due to friction lack of the paving are more likely to happen with the accretion of precipitation such as rain ( John, 1996 ) . The wet on the pavement surface may forestall vehicles ties from doing equal contact with the route surface ( Davis, 2001 ) .

2.2 Highway Safety

Safety is a necessity in every twenty-four hours ‘s making. Thus, planing and building a danger free main road is a must and guidelines to follow are provided by the guidelines from Geometric Road Design provided by the Ministry of Works Malaysia.

2.3. Pavement Type and Structure

Rigid paving is constructed of Portland cement concrete. Its stuff provides the stiff surface and longer enduring characteristic whilst flexible paving is normally constructed out of bitumen, therefore has given it the flexibleness feature, nevertheless subjected to legion types of defects in its service.

2.3.2 Rigid Pavement ( PCC )

Harmonizing to Kresge ( 2009 ) , Concrete paving gained its repute this recent old ages due to asphalt decreased in handiness. Sustainability of paving is a must sing the sum of clip taken to build or keep, and finally the costing. For that ground, legion states opted for PCC.

Comparing asphalt and concrete ( Kresge, 2009 ) , asphalt required three times more energy than concrete for life rhythm. Extremly, in term of planetary warming possible a ( CO2 Equivalents ) Aspalt give consequence 738 t/km comparison with concrete which is produce merely 674 t/km CO2 Equivalents. A stiff paving construction is composed of a hydraulic cement concrete surface class, and implicit in base and subbase classs.

High modulus of snap of PCC stuffs gives low warps when it is under lading. The stiff pavings can be analyzed by the home base theory. Rigid pavings can hold reenforcing steel, which is by and large used to manage thermic emphasiss to cut down or extinguish articulations and keep tight cleft breadths. Figure 2.2 shows a typical subdivision for a stiff paving.

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Figure 2.1 Rigid Pavement ( kresge 2009 )

2.3.3 Rigid and flexible Pavement Characteristic

The primary structural difference between a stiff and flexible paving is the mode in which each type of paving distributes traffic loads over the subgrade. A stiff paving has a really high stiffness and distributes tonss over a comparatively broad country of subgrade – a major part of the structural capacity is contributed by the slab itself ( Thomas, 2008 in Sufian 2011 ) . The burden transporting capacity of a true flexible paving is derived from the load-distributing features of a superimposed system ( Thomas,2008 in Sufian 2011 ) . Figure 2.2 shows load distribution for a typical flexible paving and a typical stiff paving.

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Figure 2.2 Typical emphasis distributions under a stiff and a flexible paving.

Pavement distributes wheel tonss over an country of subgrade. The distribution of tonss are much larger than the wheel contact country therefore to cut down the maximal subgrade emphasis to a degree which the dirt can digest without unacceptable distortion during the life of the paving ( Kamarulzaman, 2010 in Sufian 2011 ) . This is explained in Figure 2. 3.

Figure 2.3: Concept of burden spreading and the ideal paving

2.4 Skid opposition

By and large skid opposition is known as force developed when tyre prevented from revolving slides long the paving surface. It could besides come associated with vehicle tyre air force per unit area, temperature, composing, paces pattern and depth. These factors contribute to the degree of strength in the interaction generated between the tyre and the surface ( David, 2005 ) . Factor act uponing route surface clashs are shown below.

Table 2.1: Factors Influencing Road Surface Friction, David ( 2005 )

Skid opposition alterations over clip as it increases in the first two old ages following building as the roadway is worn off by traffic and unsmooth sum surfaces become exposed, so decreases over the staying pavement life as sums become more polished.

2.5 Factor Affecting Skid Resistance

Clash is dependent upon the paving macro and microtexture. Microtexture has greater influence on clash at the low velocities countries. Macrotexture becomes dominant at higher velocities, though microtexture is still of import. Macroctexture supplies the waies through which H2O can get away from between the tyre and route surface, thereby leting the microtexture to supply opposition to the comparative motion between the tyre and the route surface. ( Cement and Concrete Association of Australia )

Specifically, the skid opposition belongingss of Portland Cement Concrete ( PCC ) paving are affected by several cardinal factors including aggregative type, aggregative step ( size ) , H2O cement ration, air content, bring arounding method every bit good as the surface completing method to organize texture. Harmonizing to Meyer ( 1982 ) cited by Kelvin 2003, clash degrees developed by a paving in contact with a given tyre are mostly dependent on the paving on the paving surface texture, which can be classified into two sub-groups harmonizing to its graduated table ; macrotexture and microtexrture. Factors act uponing route surface are shown below

Table 2.2: Factors Influencing Road Surface Friction ( Sufian, 2011 )

Road

Contaminant ( fluid )

Type

Micro-texture

Macro-texture

Unevenness/Mega-texture

Chemistry of stuff

Temperature

Thermal conduction

Specific heat

Chemical construction

Viscosity

Density

Temperature

Thermal conduction

Specific heat

Film thickness

Tread form design

Rubber composing

Inflation force per unit area

Rubber hardness

Load

Skiding speed

Temperature

Thermal conduction

Specific heat

Harmonizing to CCAA ( Cement Concrete and Aggregate Australia ) 2002, skid opposition in concrete construction describes as the ability of concrete surface to supply clash to a mention Sur or slider normally measured moisture. Skid opposition is chiefly dependent upon the surface macro and microstructure. In the other manus, factor impacting skid opposition or clash and other parametric quantity in concrete paving are:

Environmental status including temperature and surface

contamination ;

Physical belongingss of paving stuff ;

Age of paving and traffic volume ;

Seasonal status such as sum of rain.

2.6. Road Surface and Texture

Macrotexture and microtexture are two type of route surface texture that influences skidding. Macrotexture is required to extinguish H2O from the contact country between the tyre and the route surface particularly at higher vehicle velocities and is determined by the size of the aggregative atoms at the route surface. The micro texture is determined by the raggedness and angular shape of the surface of the aggregative atoms. The microtexture ensures high contact force per unit areas between the sum and the tyre. ( Molenaar et al. 2004, in Sufian 2011 ) . Texture of both macro and micro as shown below.

Figure 2.6 Comparison between macrotexture and microtexture

Microtexture is the term given to the finer texture which can be felt by running a finger over the surface of a rock atom. Microtexture can assist better clash since the crisp extremums can interrupt through H2O movies and therefore let some grade of adhesion clash to be restored. When a surfacing is freshly laid, the sum atoms will normally hold acceptable microtexture. This is reduced with clip over the first few months or old ages due to the smoothing consequence of vehicle tyres, peculiarly those of heavy vehicles. It is hence necessary to measure the suitableness of an sum for a peculiar environment by subjecting it in the research lab to a fake route smoothing government.

2.7 Pavement-Tire Interaction

Pavement skid opposition is defined as the ability of a traveled surface to forestall the loss of grip ( ASTM E 867 ) . The term “ skid opposition ” can be applied to any measuring taken refering the frictional belongingss of paving surfaces. To be able to to the full grok the skid opposition of a tyre interacting with the paving surface, it is of import to understand the forces at the tire-pavement interface. These forces are complex and dependent upon tyre size, type of braking system, vehicle weight, and other vehicle specific features.

A simple block with a known speed can be used to pattern frictional forces. The value of clash can be established utilizing the force normal to the block and the counteractive force happening as a consequence of the frictional interaction between the object and the paving as shown in Figure 2.8. The immune force FR is a map of both the frictional belongingss of the surface and the alteration in speed of the sliding block. For a changeless velocity, the coefficient of clash can be computed utilizing the undermentioned equation ( Davis, 2001 )

Figure 2.8: Simplified Friction Diagrams

2.8 Friction and Texture Measurements

There are many different methods and equipment to mensurate the surface belongingss of pavings. The frictional features of paving surfaces have been measured quantitatively for many old ages. The consequences of clash proving are used to compare alterations in skid opposition over clip or to find the degree of safety of pavement surfaces.

2.8.1 Measurement of Skid Resistance

British Pendulum Test is used to prove skid opposition. It is a pendulum impact type examiner specified in ASTM E303. The British pendulum examiner is one of the simplest and cheapest instruments used in the measuring of clash features of paving surfaces.

Harmonizing to Fwa et al. , 2003, Although it is widely suggested that the measuring is mostly governed by the microtexture of the paving surface, experience has shown that the macrotexture can besides impact the measurings.

Fwa et Al. ( 2003 ) claims that the British pendulum measurings could be affected by the macrotexture of paving surfaces, aggregate spread breadth, or the figure of spreads between sums. It can besides take to deceptive consequences on rough-textured trial surfaces. Skid opposition is by and large quantified utilizing some signifier of clash measuring such as clash factor or skid figure. Harmonizing to Jayawickrama et al. , 1996, cited by Davis, 2001, the measuring is as follow:

Friction factor ( like a coefficient of clash ) :

f = F/L equation 2.1

Skid figure: SN = 100 ( degree Fahrenheit ) equation 2.2

Where: F = frictional opposition to gesture in plane of interface

L = burden perpendicular to interface

Portable examiners are available to mensurate the frictional belongingss of paving surfaces. These examiners use a pendulum or skidder theory to mensurate clash in a research lab or in the field. During proving with the British Portable Tester, a pendulum is released from a specified tallness and a gum elastic skidder attached to the terminal of the pendulum contacts the pavement surface. The deceleration of the pendulum gesture ensuing from the frictional belongingss of the trial surface is used to set up the British Pendulum Number ( BPN ) . The values of the BPN vary from zero to 140. The BPN is recorded utilizing a specially constructed graduated table located on the examiner, which measures the tallness of the pendulum after reaching the surface ( ASTM E303 ) .The table below shows some typical Skid Numbers ( the higher the SN, the better ) .

Table 2.5: Typical Skid Numbers

Skid Number

Remarks

& lt ; 30

Take step to rectify

& gt ; 30

Acceptable for low volume roads

31 – 34

Monitor paving often

& gt ; 35

Acceptable for to a great extent traveled roads

2.8.3 Surface Texture Measurement

Surface texture measuring is tested with Sand Patch Test ( ASTM E 965 ) . Measure of sand is poured onto dry route surface and spread into a round form with straightedge. As the sand is spread, it fills the low musca volitanss in the pavement surface. When the sand can non be spread further, the diameter of the resulting circle is measured. The diameter can be correlated to an mean deepness, which can be correlated to skid opposition. A texture deepness of about 1.5mm ( 0.06 inches ) is usually required for to a great extent trafficked countries.

Standard on Skid Resistance

British Portable Skid Resistance Tester is used in finding the skid opposition value of a paving taken on site or in research lab. The drift for this research came from the Transport and Research Laboratory ( TRRL ) of United Kingdom. Harmonizing to TRRL, the device simulates the clash of route surface to going vehicle of 50 km/hr. The trial gives the average skid opposition value ( SRV ) which is per centum of coefficient of clash.

Accelerated Polishing Machine on the other manus stimulates the smoothing action of tyres on route surfaces. Specimens are polished by gum elastic tyre, and so measured with pendulum to acquire the Polished Stone Value ( PSV ) . Different sites may necessitate different values of PSV, therefore, table below, as provided by TRRL specifies the minimal values of PSV for the sum used in the surfacing.

Table 2.7: Suggestion lower limit values of ‘skid opposition ‘ that is measured with the portable examiner ( TRRL )

Class

Type of site

Minimum skid opposition ( surface moisture )

A

Difficult sites such as:

Traffic circles

Decompression sicknesss with radius less than 150m on unrestricted roads

Gradients 1 in 20 or steeper of lengths & gt ; 100m

Approachs to traffic visible radiations on unrestricted roads

65

Bacillus

Expresswaies, bole and category 1 roads and to a great extent trafficked roads in urban countries ( transporting & gt ; 2000 vehicles per twenty-four hours )

55

C

All other sites

45

Temperature is besides known to act upon the measuring of skid opposition. Taking hat into consideration, figure below are to be used for corrected value.

Figure 2.14: Skid resistance/ temperature rectification relationship ( TRRL, 1969 )